Cigarette making machines commonly operate by forming a filler stream of tobacco on a suction band which then carries the filler stream into a garniture in which the filler stream is enclosed in a paper wrapper to form a continuous cigarette rod. That rod is then cut at regular intervals into predetermined lengths. Examples of such a machine are described in British patents Nos. 2023401 and 2087213.
Suction bands for cigarette making machines have in the past commonly been made of metal (usually Nickel) formed with perforations so as to be air-pervious, or have been in a woven nylon form. Both of these band constructions are fairly expensive.
A suction band according to the present invention, for use in a cigarette making machine for conveying a cigarette filler stream, comprises a tape of heat-softenable plastics material wound so as to produce a multi-layer endless band and having perforations of which the edges of the adjacent perforations in adjacent tape layers are welded or fused together so as to join together the tape layers to form a cohesive perforated band.
The perforations are preferably formed by pins which are heated so as to melt and thus weld together the adjacent tape layers while forming the perforations. During manufacture the pins preferably penetrate the band from the inside so as to deform outwards melted portions of the band, thus forming a rough surface helpful in driving the tobacco forward during use. For example, the perforations may be formed by pins with their axes inclined to the normal (with respect to the plane of the adjacent portion of the band) so as to form annular crater-like protrusions around the perforations which are higher on the downstream sides of the perforations than on the upstream sides (or vice versa), the term xe2x80x9cupstreamxe2x80x9d being used here in relation to the intended direction of movement of the band during use; such protrusions minimise any tendency for strands of tobacco to block the perforations and thus reduce the air flow through them.
Alternatively, pins may be used to form the perforations and may be ultrasonically vibrated so as to melt or fuse the edges of the perforations.
Another possibility is that the perforations may be formed by a laser. In this case in particular, at least the outer surface of the band may be made rough or uneven, before perforating, to facilitate forward driving of the tobacco. For example, the band may be driven between pinching rolls (heated or ultrasonically vibrated) to form a dimpled, undulating or knurled surface on the band.
An ultrasonic device may in any event be used to weld or fuse together the tape layers around their entire surfaces or along longitudinally striped areas (including, for example, the band edges), before, during or after the perforating stage.
In the case of a laser perforator, the pattern and/or size of the perforations can readily be changed to suit, for example, the needs arising with different tobaccos or in different cigarette making machines.
The outer end of the tape preferably lies in a trailing fashion in relation to the direction of movement of the band. It may be secured by additional welding along the end edge (eg by a hot blade or laser) or may be held in position purely or mainly by the adjacent perforations.
For economy of manufacture, a multiple-width band may be formed initially, with longitudinally extending perforated areas separated by non-perforated areas which will form the edges of the individual bands. Subsequent slitting of the multiple-width band to produce individual bands may be achieved by a hot disc knife, laser or ultrasonic device so as to weld the edges of the bands.